The present invention relates to a cutting insert including cubic boron nitride with an excellent wear resistance and maintained resistance to chipping and edge fracture when machining hard materials like hardened steel and alike.
Cubic boron nitride (cBN)-based ceramics sintered under high pressure and high temperature are known.
Generally, cBN-based materials for hard part machining have cBN as the hard dispersed phase and a ceramic binder to form a sintered hard cutting tool. The cBN material for cutting tools normally has a cBN content ranging from 40 to 90 vol-% and a ceramic binder phase consisting generally of a nitride, carbonitride or carbide of titanium with less amounts of borides of Ti, W, Co, Al or a solid solution of these, alumina and other unavoidable reaction products. By varying the relative amounts of the ingredients, cBN tools can be designed for optimum performance in different applications, e.g., continuous or interrupted cutting. cBN tools with relatively high cBN content are recommended for toughness demanding interrupted to heavy interrupted cutting applications, whereas high ceramic binder content gives the high wear resistance necessary in continuous cutting.
Thus, in wear demanding cutting applications run at high cutting speed and low cutting depth, and a feed ranging from continuous to lightly interrupted, a low cBN content is chosen. There is, however, a need of further improved cBN-based tools since a higher productivity with reduced costs is required from the industry. Generally this implies higher cutting speeds and in particular higher cutting depths and feeds. However, during continuous machining, the entrance and exit of the insert cause a sudden extra load at the cutting edge and machine instability may cause an intermittent behavior. Both the effects may result in unacceptable edge failure. Consequently, cutting tools with improved wear resistance without loss in edge failure resistance are desired, in order to meet the demands from the machining industry.
In the past it has been proposed to use an intermediate adhesion phase between the ceramic binder and the hard dispersed phase (U.S. Pat. No. 7,112,235) in order to increase chipping resistance. A bonding phase surrounding the cBN grains has also been proposed (U.S. Pat. No. 6,316,094) in order to prevent a direct cBN-cBN contact. The bonding phase is formed due to a chemical reaction between cBN or B2O3 residuals coating the cBN grains and the ceramic binder forming TiB2. Furthermore, cBN grains have been pre-coated by a nitride or boride of Ti and Al by a PVD-process in order to enhance the reinforcing rim surrounding the cBN grains (U.S. Pat. No. 6,265,337). U.S. Pat. No. 4,911,756 discloses a sintered compact containing 50 to 70 vol-% cBN and a binder containing 25 to 50 wt-% Al, one or more Ti compounds, and W or one or more W compounds, whereby the W content in the binder is 4 to 40 wt-%.
WO 2006/046125 discloses a cBN compact with a secondary hard phase of TiCN, TiC, TiN and mixtures and solid solutions. The TiB2 peak height (measured as the percentage of the cBN peak height) is disclosed to be from 2.5 to less than 12% using the measurement technique described in that publication.